Hypophysectomy and hormne replacement therapy have been the classical methods to study the hormonal control of the testis. With these techniques it has proved difficult to examine the respective roles of FSH and LH. The use of specific antiserum to each of the gonadotropins is a better method to dissect the respective roles of FSH and LH in spermatogenesis. We plan to examine the dependence of various parameters on each of the gonadotropins during germ cell development in the immature rat and during adult rat spermatogenesis. The tool that we propose to use is highly specific antiserum to either FSH or LH. Our preliminary evidence suggests that in the rat FSH is required for the inititation of spermatogenesis but that is may not be required for maintenance in the adult. The hormonal response of the monkey's testis may be closer to that of human's but both monkey and human may be different from rodents. Therefore, we propose to utilize antiserum to ovine FSH in efforts to neutralize endogenous FSH in the monkey. Our objective in this part of the work is to determine whether maintenance of normal spermatogenesis in the adult monkey is dependent upon FSH. This has obvious significance in humans for the development of a contraceptive agent that depends upon selective reduction of FSH. We plan to develop methods so that we can measure free ganodotropin by radioimmunoassay, in the serum of our experimental animals treated with anti-gonadotropic serum, is passive immunization experiments.